CHAPTER XV RODENTIA-----TILLODONTIA Order IX. RODKNTIA1 SMALL to moderately large animals, furry, sometimes with spines. Toes with nails of a claw-like character, or sometimes approach- ing hoofs. Usually plantigrade, and only occasionally and partly carnivorous. Canine teeth absent; incisors long and strong, growing from persistent pulps, and with enamel only or chiefly on the anterior face, producing a chisel-shaped edge; molars few (two to six), separated from the incisors by a wide diastema. Caecum (nearly always present) very large, and often complicated in structure. Brain, if not smooth, with few furrows, the hemispheres not overlapping the cerebellum. Surface of skull rather flat; orbits not separated from temporal fossae; malar bone in middle of zygomatic arch; palate very narrow, with elongated incisive foramina; articular surface for lower jaw antero-posteriorly elongated. Clavicles generally present. Testes generally abdominal. Placenta deciduate, and discoidal in form. The Rodents are a very large assemblage of usually small, sometimes cjuite minute, creatures, embracing an enormous number of living generic types. They are distributed all over the world, including the Australian region, and, being small and often nocturnal, and by no means particular in their diet, have managed to thrive and multiply to a greater extent than any other group of living mammals. They are chiefly terrestrial creatures, and often burrow or live in ready-made burrows. 1 See especially Tullberg, " tTeber das System der Nagethiere," Act. Ale. Upsala, 1899 ; and Alston, Proe. &&oL Soe. 1875, p. 61; and for nomenclature, Thomas, Proc* ZooL Soc. 1896, p. 1012 ; and Palmer, Proc. JSiol. Soe. WasJiington, xi. 1897, p. 241.